Conventionally, there are mainly provided an angle rotor and a swinging rotor as rotors used for a centrifugal separator. In the angle rotor, a constant value of an angle is used for the angle of a tube hole for holding each tube containing a sample to carry out a centrifugal treatment. The swinging rotor is formed by a rotor yoke and a bucket. The bucket is used to accommodate tubes each containing a sample, and detachably and swingably attached to the rotor yoke. The tubes are accommodated in the bucket while they are held in a tube rack. The bucket is swung up by the centrifugal force up to an angle of 0 to 90° along with the rotation of the rotor yoke.
The tubes used for the swinging rotor are generally, mainly made of glass or plastic.
In a conventional tube rack, one or a plurality of individual tube holes is formed to hold a tube. A tube containing a sample is inserted into the tube hole, and held.
There are mainly two reasons why the tube is inserted into the individual tube hole. The first reason is to prevent, if one of the tubes is damaged during the centrifugal treatment, any effect of the damage from spreading to other adjacent tubes.
The second reason is to keep the sample contained in the damaged tube within the tube rack so as to prevent toxic substance and toxic bacteria from adhering to the bucket and the like.
Each tube hole of the tube rack is often formed as a non-through hole conforming to the outer shape and bottom shape of the tube, that is, a blind hole shape. The reason for this is to prevent the tube from being deformed or damaged by the centrifugal force.
In general, tube racks are made of plastic, and some are cut out by machining and some are formed by resin molding. Some of the tube racks formed by resin molding include tube holes each divided into an upper portion, middle portion, and bottom surface, and some others include tube holes each including no middle portion and supporting a tube by only an upper portion and bottom surface.
There is provided a conventional tube rack in which a bottom rubber portion (elastic body) is inserted into the bottom surface of a tube hole. This tube rack is used when the strength of the tube bottom surface is low and the bottom shape varies for each tube.
When the bottom shape of a tube hole contacting a tube in the tube rack is considerably different from the bottom shape of the tube, an excessive force is applied to a portion of the tube bottom surface, and the tube bottom portion is unwantedly deformed or damaged. As for the tube rack in which a bottom rubber portion is inserted into the bottom surface of the tube hole, the bottom rubber portion can be deformed in accordance with the shape of the tube bottom surface, and it is thus possible to prevent an excessive force from being applied to the portion of the tube bottom surface.
As a conventional tube rack including a bottom rubber portion, there is provided, for example, a tube rack described in patent literature 1. The bottom rubber portion disclosed in patent literature 1 includes a film-like projection or fin-shaped projection around a cushion portion contacting the bottom portion of the tube. An arrangement in which the film-like projection or fin-shaped projection is pressed against the hole wall of the tube hole is adopted. By forming the film-like projection or fin-shaped projection in the bottom rubber portion, it is possible to prevent, when the tube is removed from the tube hole, the bottom rubber portion from being separated from the tube hole together with the tube.